ld: Initial DT_RELR support

Add a -z pack-relative-relocs option to enable DT_RELR and create a
relr.dyn section for DT_RELR.  DT_RELR is implemented with the linker
relaxation infrastructure, but it doesn't require the --relax option
enabled.  -z pack-relative-relocs implies -z combreloc.  -z nocombreloc
implies -z nopack-relative-relocs.

-z pack-relative-relocs is chosen over the similar option in lld,
--pack-dyn-relocs=relr, to implement a glibc binary lockout mechanism
with a special glibc version symbol, to avoid random crashes of DT_RELR
binaries with the existing glibc binaries.

bfd/

	* elf-bfd.h (elf_link_hash_table): Add srelrdyn.
	* elflink.c (_bfd_elf_link_create_dynamic_sections): Create a
	.relr.dyn section for DT_RELR.

include/

	* bfdlink.h (bfd_link_info): Add enable_dt_relr.

ld/

	* News: Mention -z pack-relative-relocs and
	-z nopack-relative-relocs.
	* ld.texi: Document -z pack-relative-relocs and
	-z nopack-relative-relocs.
	* ldelf.c (ldelf_after_parse): Disable DT_RELR if not building
	PIE nor shared library.  Add 3 spare dynamic tags for DT_RELR,
	DT_RELRSZ and DT_RELRENT.
	* ldlang.c (lang_relax_sections): Also enable relaxation if
	DT_RELR is enabled.
	* emulparams/elf32_x86_64.sh: Source dt-relr.sh.
	* emulparams/elf_i386.sh: Likewise.
	* emulparams/elf_x86_64.sh: Likewise.
	* emulparams/dt-relr.sh: New file.
	* scripttempl/elf.sc: Support .relr.dyn.

4 files changed, 21 insertions, 0 deletions

diff --git a/ld/emulparams/dt-relr.sh b/ld/emulparams/dt-relr.sh
new file mode 100644
index 0000000..b2b403c
--- /dev/null
+++ b/ld/emulparams/dt-relr.sh
@@ -0,0 +1,18 @@
+HAVE_DT_RELR=yes
+PARSE_AND_LIST_OPTIONS_PACK_RELATIVE_RELOCS='
+  fprintf (file, _("\
+  -z pack-relative-relocs     Pack relative relocations\n"));
+  fprintf (file, _("\
+  -z nopack-relative-relocs   Do not pack relative relocations (default)\n"));
+'
+
+PARSE_AND_LIST_ARGS_CASE_Z_PACK_RELATIVE_RELOCS='
+      else if (strcmp (optarg, "pack-relative-relocs") == 0)
+	link_info.enable_dt_relr = true;
+      else if (strcmp (optarg, "nopack-relative-relocs") == 0)
+	link_info.enable_dt_relr = false;
+'
+
+
+PARSE_AND_LIST_OPTIONS="$PARSE_AND_LIST_OPTIONS $PARSE_AND_LIST_OPTIONS_PACK_RELATIVE_RELOCS"
+PARSE_AND_LIST_ARGS_CASE_Z="$PARSE_AND_LIST_ARGS_CASE_Z $PARSE_AND_LIST_ARGS_CASE_Z_PACK_RELATIVE_RELOCS"
diff --git a/ld/emulparams/elf32_x86_64.sh b/ld/emulparams/elf32_x86_64.sh
index ac0a7aa..4bff412 100644
--- a/ld/emulparams/elf32_x86_64.sh
+++ b/ld/emulparams/elf32_x86_64.sh
@@ -7,6 +7,7 @@ source_sh ${srcdir}/emulparams/cet.sh
 source_sh ${srcdir}/emulparams/x86-report-relative.sh
 source_sh ${srcdir}/emulparams/x86-64-level.sh
 source_sh ${srcdir}/emulparams/static.sh
+source_sh ${srcdir}/emulparams/dt-relr.sh
 SCRIPT_NAME=elf
 ELFSIZE=32
 OUTPUT_FORMAT="elf32-x86-64"
diff --git a/ld/emulparams/elf_i386.sh b/ld/emulparams/elf_i386.sh
index 98532e5..ae17bb4 100644
--- a/ld/emulparams/elf_i386.sh
+++ b/ld/emulparams/elf_i386.sh
@@ -6,6 +6,7 @@ source_sh ${srcdir}/emulparams/cet.sh
 source_sh ${srcdir}/emulparams/x86-report-relative.sh
 source_sh ${srcdir}/emulparams/x86-64-level.sh
 source_sh ${srcdir}/emulparams/static.sh
+source_sh ${srcdir}/emulparams/dt-relr.sh
 SCRIPT_NAME=elf
 OUTPUT_FORMAT="elf32-i386"
 NO_RELA_RELOCS=yes
diff --git a/ld/emulparams/elf_x86_64.sh b/ld/emulparams/elf_x86_64.sh
index 48d0974..5f2743e 100644
--- a/ld/emulparams/elf_x86_64.sh
+++ b/ld/emulparams/elf_x86_64.sh
@@ -8,6 +8,7 @@ source_sh ${srcdir}/emulparams/x86-report-relative.sh
 source_sh ${srcdir}/emulparams/x86-64-level.sh
 source_sh ${srcdir}/emulparams/x86-64-lam.sh
 source_sh ${srcdir}/emulparams/static.sh
+source_sh ${srcdir}/emulparams/dt-relr.sh
 SCRIPT_NAME=elf
 ELFSIZE=64
 OUTPUT_FORMAT="elf64-x86-64"